Edge or line jaggedness is a common problem associated with the printing of binary image data, since forced dot placement on a fixed grid can result in visible irregularities. As a result, different approaches have been implemented to smooth line jaggedness, including template matching and outline extraction. Both methods typically use a bitmap as an input file. Digital processing operations are performed on the input file to produce an enhanced image output file, which is subsequently supplied to a print head to produce a hard copy of the image.
Some difficulties arise, however, when using template matching or outline extraction methods to provide edge enhancement. For example, the number of templates employed during template matching is usually limited to maintain acceptable processing speeds. However, if the number of templates is severely restricted, some number of the patterns within the input file bitmap will not match the available templates, and edge resolution enhancement cannot be performed regardless of the resulting image quality.
During outline extraction, variable dot sizes are used to fill in character outlines. However, the filling process typically requires an increasing number of resources as smaller fonts are employed. In addition, closely spaced, thin lines, such as those which appear in a graph, may be broadened to the point of merger, resulting in a perceivable reduction in image resolution.
Attempting to smooth jaggedness in color images before they are printed increases the number of problems encountered. For example, the unwanted results of managing multiple color planes can include the disruption of halftone data and undesirable color shifting at the edges of the images being processed. Processing information from several color planes can also require resources beyond those available during various parts of the printing process.